Merge pull request #1282 from vedantk/cherry

[LiveDebugValues] Add cutoffs to avoid pathological behavior

llvm/lib/CodeGen/LiveDebugValues.cpp

@@ -80,6 +80,18 @@ using namespace llvm;
 STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
 STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed");
 
+// Options to prevent pathological compile-time behavior. If InputBBLimit and
+// InputDbgValueLimit are both exceeded, range extension is disabled.
+static cl::opt<unsigned> InputBBLimit(
+    "livedebugvalues-input-bb-limit",
+    cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
+    cl::init(10000), cl::Hidden);
+static cl::opt<unsigned> InputDbgValueLimit(
+    "livedebugvalues-input-dbg-value-limit",
+    cl::desc(
+        "Maximum input DBG_VALUE insts supported by debug range extension"),
+    cl::init(50000), cl::Hidden);
+
 // If @MI is a DBG_VALUE with debug value described by a defined
 // register, returns the number of this register. In the other case, returns 0.
 static Register isDbgValueDescribedByReg(const MachineInstr &MI) {
@@ -1752,6 +1764,22 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
     Worklist.push(RPONumber);
     ++RPONumber;
   }
+
+  if (RPONumber > InputBBLimit) {
+    unsigned NumInputDbgValues = 0;
+    for (auto &MBB : MF)
+      for (auto &MI : MBB)
+        if (MI.isDebugValue())
+          ++NumInputDbgValues;
+    if (NumInputDbgValues > InputDbgValueLimit) {
+      LLVM_DEBUG(dbgs() << "Disabling LiveDebugValues: " << MF.getName()
+                        << " has " << RPONumber << " basic blocks and "
+                        << NumInputDbgValues
+                        << " input DBG_VALUEs, exceeding limits.\n");
+      return false;
+    }
+  }
+
   // This is a standard "union of predecessor outs" dataflow problem.
   // To solve it, we perform join() and process() using the two worklist method
   // until the ranges converge.

llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir

@@ -0,0 +1,99 @@
+# Test cutoffs for livedebugvalues debug range extension.
+# Disable LDV if the input-bb-limit AND the input-dbg-value-limit are both exceeded.
+
+# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
+# RUN:   -livedebugvalues-input-bb-limit=1 \
+# RUN:   -livedebugvalues-input-dbg-value-limit=1 \
+# RUN:   | FileCheck %s -check-prefix=LDV-DISABLED
+
+# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
+# RUN:   -livedebugvalues-input-bb-limit=1 \
+# RUN:   -livedebugvalues-input-dbg-value-limit=10 \
+# RUN:   | FileCheck %s -check-prefix=LDV-ENABLED
+
+# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
+# RUN:   -livedebugvalues-input-bb-limit=10 \
+# RUN:   -livedebugvalues-input-dbg-value-limit=1 \
+# RUN:   | FileCheck %s -check-prefix=LDV-ENABLED
+
+# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
+# RUN:   -livedebugvalues-input-bb-limit=10 \
+# RUN:   -livedebugvalues-input-dbg-value-limit=10 \
+# RUN:   | FileCheck %s -check-prefix=LDV-ENABLED
+
+# LDV-DISABLED-LABEL: bb.1.exit
+# LDV-DISABLED-NEXT: $edi = MOV32rm
+
+# LDV-ENABLED-LABEL: bb.1.exit
+# LDV-ENABLED-NEXT: DBG_VALUE $rsp, 0, {{.*}}, !DIExpression(DW_OP_plus_uconst, 4)
+# LDV-ENABLED-NEXT: $edi = MOV32rm
+
+--- |
+  target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+  declare i32 @use(i32)
+
+  define i32 @foo(i32 %x) !dbg !6 {
+  entry:
+    %y = add i32 %x, %x, !dbg !12
+    call void @llvm.dbg.value(metadata i32 %y, metadata !9, metadata !DIExpression()), !dbg !12
+    br label %exit, !dbg !13
+
+  exit:                                             ; preds = %entry
+    %z = call i32 @use(i32 %y), !dbg !14
+    call void @llvm.dbg.value(metadata i32 %z, metadata !11, metadata !DIExpression()), !dbg !14
+    ret i32 %z, !dbg !15
+  }
+
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.debugify = !{!3, !4}
+  !llvm.module.flags = !{!5}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+  !1 = !DIFile(filename: "/tmp/t.ll", directory: "/")
+  !2 = !{}
+  !3 = !{i32 4}
+  !4 = !{i32 2}
+  !5 = !{i32 2, !"Debug Info Version", i32 3}
+  !6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+  !7 = !DISubroutineType(types: !2)
+  !8 = !{!9, !11}
+  !9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+  !10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+  !11 = !DILocalVariable(name: "2", scope: !6, file: !1, line: 3, type: !10)
+  !12 = !DILocation(line: 1, column: 1, scope: !6)
+  !13 = !DILocation(line: 2, column: 1, scope: !6)
+  !14 = !DILocation(line: 3, column: 1, scope: !6)
+  !15 = !DILocation(line: 4, column: 1, scope: !6)
+
+...
+---
+name:            foo
+liveins:
+  - { reg: '$edi', virtual-reg: '' }
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.0.entry:
+    successors: %bb.1(0x80000000)
+    liveins: $edi
+
+    frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
+    CFI_INSTRUCTION def_cfa_offset 16
+    renamable $edi = ADD32rr renamable $edi, killed renamable $edi, implicit-def $eflags, debug-location !12
+    DBG_VALUE renamable $edi, $noreg, !9, !DIExpression(), debug-location !12
+    MOV32mr $rsp, 1, $noreg, 4, $noreg, killed $edi :: (store 4 into %stack.0)
+    DBG_VALUE $rsp, 0, !9, !DIExpression(DW_OP_plus_uconst, 4), debug-location !12
+
+  bb.1.exit:
+    $edi = MOV32rm $rsp, 1, $noreg, 4, $noreg :: (load 4 from %stack.0)
+    CALL64pcrel32 @use, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit-def $eax, debug-location !14
+    DBG_VALUE renamable $eax, $noreg, !11, !DIExpression(), debug-location !14
+    $rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !15
+    RETQ implicit killed $eax, debug-location !15
+
+...